• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.2B
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• pp.124-132
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• 2007

Where a wireless LAN and a cellular network coexist, a mobile node has to experience vertical handoffs to move between them. Immediately after the vertical handoffs, TCP must need adaptation latency to adjust its congestion window to the proper size at a newly arrived network to use full of a new end-to-end available bandwidth. Even though SACK TCP has the best performance among other regular TCPs in the previous studies, it still cannot use full of the new available bandwidth quickly due to its inefficient increasing way of congestion window. BIC TCP, that becomes a popular TCP in long fat networks, has great feature working well against vertical handoffs by increasing congestion window exponentially with TCP connection sustained. In this paper, we derive adaptation latency of SACK TCP and BIC TCP numerically, and verify them by simulations. We also find that the shorter adaptation latency of BIC TCP produces higher throughput than SACK TCP on vertical handoffs. Consequently, to get higher performance on vertical handoff situations, we propose to use BIC TCP.

• The KIPS Transactions:PartC
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• v.10C no.7
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• pp.943-954
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• 2003

The mobile telecommunication system has been growing exponentially after 1990s due to the high population in a city and the growth of mobile user. In this time, the current mobile system mainly concentrates on the voice communication. However, in the next generation, mobile users want to get very diverse services via mobile terminal such as the Internet access, web access, multimedia communication, and etc. For this reason, the next generation system, such as the UMTS (Universal Mobile Telecommunication Services) system, has to support the packet data service and it will play the major role in the system. By the way, since the Web service is based on TCP, most of the Internet traffic TCP traffic. Therefore, efficient transmission of TCP traffic will take very important role in the performance of packet data service. There are many researches about improving TCP performance over wireless network. In those schemes, the UMTS system adapts the link layer retransmission scheme. However, there are rarely studies about the exact performance of the link layer retransmission scheme in the face of dynamic changes of wireless environment over the UMTS system. The dynamic changes of wireless environment, such as wireless bandwidth, can degrade TCP performance directly. So, in this paper, we simulate and analyze the TCP performance in the UMTS system with dynamic wireless environments. Then, we propose a simple scheme for minimizing TCP performance degradation. As a result of simulation, we can find that when wireless environment is changed dynamically, the probability of TCP timeout is increased, and the TCP performance is degraded very much. In this situation, the proposed simple scheme shows good performance. It saves wireless resources and reduces the degradation of TCP performance without large overhead of the base station.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.5 no.5
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• pp.923-930
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• 2001

In this paper, in order to improve the performance of TCP short traffic services in wireless Internet environments, the Split-ACKs(SPACK) scheme is proposed. In wireless networks, unlike wired networks, packet losses will occur more often due to high bit error rates. Therefore, each packet loss over wireless links results in congestion control procedure of TCP being invoked at the source. This causes severe end-to-end performance degradation of TCP. In this paper, to alleviate the TCP performance, the SPACK method, split acknowledgement packets in the base station, is proposed. Using computer simulation, the performance of TCP using SPACK is analyzed and shows better performance than traditional TCP protocol.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2000.10a
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• pp.307-312
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• 2000

In this paper, in order to improve the performance of TCP short traffic services in wireless Internet environments, the Split-ACKs(SPACK) scheme is proposed. In wireless networks, unlike wired networks, packet losses will occur more often due to high bit error rates. Therefore, each packet loss over wireless links results in congestion control procedure of TCP being invoked at the source. This causes severs end-to-end performance degradation of TCP. In this paper, to alleviate the TCP performance, the SPACK method split acknowledgement packets in the base station is proposed. Using computer simulation the performance of TCP using SPACK is analyzed and shows better performance than traditional TCP protocol.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.42 no.1
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• pp.121-127
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• 2017

In the land mobile satellite (LMS) communication, a hybrid satellite-terrestrial relay networks (HSTRNs) using a maximal ratio combining (MRC) scheme are widely used to enhance the quality of signal from a satellite. In this paper, we derive equations for the TCP throughput and the spectral efficiency in the HSTRN and analyze results of the performance evaluation for TCP in various environments. In the simulation results, it is shown that increasing the number of terrestrial relays can enhance the TCP throughput and spectral efficiency thanks to the MRC scheme. However, the usage of the static number of terrestrial relays considering no channel states would cause the overhead. Furthermore, it has a limitation to enhance the network performance by only MRC scheme in HSTRN because the TCP performance is sensitive to the packet los rate. Therefore, we discuss the possible solutions that can additionally enhance the network performance and reduce the overhead.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.23 no.7
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• pp.1744-1754
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• 1998

In this paper, the data service protocol which could support data service more efficiently between mobile host and fixed host in wire network is investigated. Wireless link has high bit error rate compared with wire link. Therefore, TCP performance for the data service is degraded in wire and wireless interworking environment. Thus, to reduce performance degradation. Interworking module withsimple protocol processing function is proposed. This, interworking module analyzes the hearder information of TCP fram. If received TCP freame is a duplicated frame, TCP frame is discared. Also, if interworking moudule receives retransmission request frame is a duplicated frame, TCP freme is discarded. Also, if interworking module receives retansmission request frame, interworking module performs retransmission procedure. According to simulation results, the proposed IWF shows better performance than traditional IWF in view of delay and throughput in the wire and wireless interworking environments.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.3A
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• pp.221-231
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• 2006

TCP is needed as a transport protocol to provide reliable end-to-end message delivery for MANETs in order to achieve a smooth integration with the fixed Internet. Particularly, TCP has its variants, namely TCP-Reno and TCP-Vegas. However, there has been no research work on extensive performance comparison of TCP-Reno and TCP-Vegas over AODV and OLSR. This paper is the first trial to perform the research by using ns-2 simulator. Through the extensive simulations, we found that which to select among routing protocols is more important than which to select among TCP variants, because the performance difference between TCP-Reno and TCP-Vegas over uy selected routing protocol is not so much outstanding. Particularly, TCP-Vegas relies on an accurate BaseRTT estimation in order to decide the sending rate of a TCP Sender. However, it cannot be directly applied to MANET because a route change makes the Base an used over a Previous Path obsolete. Therefore, we propose a technique for improving the performance of TCP-Vegas by considering the route change, and show the performance improvement through simulation study.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.28 no.12B
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• pp.1106-1114
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• 2003

Several analytic models describe transmission control protocol (TCP) performance such as steady-state throughput as an averaged ratio of number of transmissions to latency. For more detailed analysis of TCP latency, the latency during packet losses are recovered should be considered. In this paper, we derive the expected duration of loss recovery latency considering the number of packet losses recovered by retransmissions. Based on the numerical results verified by simulations, TCP using selective acknowledgement (SACK) option is more effective than TCP NewReno from the aspect of loss recovery latency.

• Proceedings of the Korea Information Processing Society Conference
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• 2009.11a
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• pp.503-504
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• 2009

최근 차세대 휴대 인터넷 기술로 주목받고 있는 WiMAX 네트워크의 성능을 향상시키기 위한 연구가 많이 진행되고 있다. WiMAX 네트워크을 이용하는 대부분의 응용들이 TCP/IP 계층을 사용하며 기존 TCP 전송기법들이 유선망을 주로 고려한 한계가 있으므로, WiMAX 네트워크 상에서의 전송 계층 성능 향상에 대한 연구의 필요성이 증대되고 있다. 본 논문에서는 실제 WiMAX 네트워크 상에서 기존 유선 네트워크에서 사용되던 TCP Reno, Veno, Westwood, Cubic 등의 TCP 혼잡제어 알고리즘들의 성능을 측정하고 비교, 분석하여 WiMAX 네트워크에서 TCP의 동작 특성을 살펴본다.

• Journal of KIISE:Information Networking
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• v.27 no.1
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• pp.76-87
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• 2000

ATM is a key technology of integration of multimedia service. Recently, Many study have been concentrated on performance testing for evaluation network performance are stronger everyday. The performance testing is on evaluation of maximal throughput of network by measuring and analyzing of various performance parameters. There are two ways to test ATM network performance; one is using QoS in cell level on the point of network's view, and the other is using metric in frame level in the point of user's view. And, the standardization process is also under way. In this paper, we derive a performance requirement of TCP in TCP/IP data transmission over ATM UBR service. By applying the derived requirements to ATM and packet networks, we evaluate the performance of TCP over UBR based on the result of our simulations. Therefore, we evaluate the result of simulation and find degradation of network throughput by interaction between TCP congestion control and ATM cell drop policy. So we suggest the accelerated Vegas that modify traditional TCP Vegas in congestion control mechanism for batter network throughput.